In thermal dye sublimation printing, it is generally well known to render images by heating and pressing one or more donor materials such as a colorant (e.g., a dye) or other coating against a receiver medium having a colorant receiving layer. The heat is generally supplied by a thermal print head having an array of modulated heating elements. The donor materials are typically provided in sized donor patches on a movable web known as a donor ribbon. The donor patches are organized on the ribbon into donor sets; each set containing all of the donor patches that are to be used to record an image on the receiver web. For full color images, multiple color dye patches can be used, such as yellow, magenta, and cyan donor dye patches. Arrangements of other color patches can be used in like fashion within a donor set. Additionally, each donor set can include an overcoat or sealant layer.
Thermal printers offer a wide range of advantages in photographic printing including the provision of truly continuous tone scale variation and the ability to deposit, as a part of the printing process a protective overcoat layer to protect the images formed thereby from mechanical and environmental damage and fading. Accordingly, many photographic kiosks, portable printers, and home photo printers currently use thermal printing technology.
For low volume printing applications, such as portable or home thermal printing systems, these types of printers are adapted to print on individual sheets of receiver media. Thermal printing systems that are used for large volume applications, such as photographic kiosks, commonly utilize roll-fed receiver media.
Some current thermal printers utilize high efficiency donor ribbons and receivers, where small amounts of transferable dye remains on the transferable dye ribbon patch when printing high densities. High efficiency donors have enough dye to create satisfactory D-max densities on designated high efficiency receivers at a reduced level of thermal energy. These printers use a reduced amount of energy provided by the thermal print head to transfer the proper amount of dye to produce the correct maximum density color image. Printing methods and systems that utilize high efficiency donor ribbons and receivers use less energy and produce less heat, which reduces environmental impacts, energy consumption, and extends the operating life of the print head. Using standard thermal donor ribbons and receivers in a printing system designed to utilize high efficiency donor ribbons and receivers can cause premature wear and damage to the print head. These conditions can be caused by running the print head hotter than intended. Standard donor ribbons tend to be more abrasive than high efficiency donor ribbons causing premature wear. Using standard donor ribbons and receivers in printing systems designed to use high efficiency donor ribbons and receivers also causes reduction in image quality and requires re-calibration of the printer to compensate for this media type in order to produce an acceptable print.
In addition, requiring less energy to make high quality thermal prints not only reduces energy costs, it also enhances applications such as portability for on-site event imaging, stand alone and user operated retail kiosks, and home printing. These applications also make it difficult to calibrate the printer since a procedure must be performed by a knowledgeable user or trained operator that also requires a scanner, densitometer, or spectrophotometer to read a printed calibration target. The calibration target readings have to be entered back into the printer or a computer connected to the printer in order for the printer to be calibrated. Printer calibration is beneficial when replacing expended donor ribbons and receivers to compensate for manufacturing lot variations in media and or changes in ambient conditions, such as transporting the printer from and indoor to outdoor venue. However, typical calibration procedures waste time, materials, and require expensive ancillary equipment.
Some thermal printing systems incorporate optical emitters and sensors which are used to measure and analyze the color and density of thermal donor ribbon patches to determine that the correct donor ribbon patch color is in position in order to print the appropriate cyan, magenta, yellow color image layer and protective clear overcoat layer.
There remains a need in the art for a method to calibrate a high efficiency thermal printing system for printing color images which uses a thermal printer having high efficiency dye donor ribbon, having a repeating series of spaced patches of yellow, magenta and cyan colored heat transferable dyes and a protective clear overcoat layer, on to a high efficiency dye receiving sheet.